The present invention relates to the field of the detection of alpha particle aerosols contained in the atmosphere and particularly to the monitoring of laboratories in which work personnel handle plutonium or transuranium elements which emit alpha radiation.
In general terms, it is well known that the measurement of atmospheric contamination by alpha particle aerosols always comes up against the problem of ambient background noise due to the presence of radon and its daughter nuclei, which are normally present in the atmosphere and also alpha emitters. Thus, on collecting for analysis purposes all the alpha emitting particles, a falsified result is obtained, which does not give a correct picture of the dangers actually met with by a person breathing in the analysed atmosphere. Thus, whereas alpha particles due to radon and its daughter nuclei in the neutral atmosphere are normally inhaled by the human being without serious physiological consequences, plutonium 239 and its transuranium elements are highly toxic materials havng a very long decap period, i.e. by definition very dangerous when inhaled and fixed on organs of the human body.
It is for this reason that up to now an attempt has been made to separate in alpha contamination signals, those which are due to the background noise of radon daughter nuclei and those due to accidental chemical pollution. Two methods have hitherto been used, but they suffer from disadvantages making them very difficult to use.
The first of these methods consists of using alpha spectrometry, i.e. sorting the alpha particles as a function of their wavelength. This requires relatively heavy, expensive equipment and the physical and electronic processing required lasts a time which, in an emergency, could constitute an unacceptable delay.
The second method consists of carrying out this separation by studying the radioactive decay times of the different alpha particles, which permits a good separation of those emitted by radon daughter nuclei, but the analysis of the results takes a long time and involves a delay of about a day, which is prohibitive when it is wished to carry out rapid, continuous monitoring in a laboratory of the quality of the air inhaled by personnel.
Finally, the two aforementioned methods require the use of relatively complex, costly electronic equipment, which makes it completely impossible to produce a detection apparatus, which is autonomous and can be worn or carried by each person working in the laboratory.